The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent the work is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.
Block-based motion compensation, transform, and quantization are broadly employed for video compression to improve performance of video communication systems. However, due to coarse quantization and motion compensation, compression noise can be introduced which causes artifacts, such as blocking, ringing, and blurring in reconstructed pictures. In-loop filters can be employed to reduce the compression noise, which can not only improve quality of decoded pictures, but also provide high quality reference pictures for succeeding pictures to save coding bits. A non-local adaptive loop filter is one type of such in-loop filter.